The present invention relates to a fluorescent luminous tube; and, more particularly, to a fluorescent luminous tube having an improved connecting structure for cathode filaments.
FIG. 5A shows a plan view (a partial cross-sectional view) of a conventional fluorescent luminous tube (or fluorescent display device), and FIGS. 5B and 5C depict schematic views of a connecting structure for cathode filaments thereof.
Anode electrodes 63 on which a fluorescent material is deposited are formed on an anode substrate 61 made of an insulating material such as a glass. Grids 64 are arranged between the anode electrodes 63 and filaments 60 to control electrons emitted from the filaments 60 to the anode electrodes 63. The filaments 60 are tightly suspended between an anchor 661 and a support 662 so that a display region 65 is covered. The anchor 661 and the support 662 are fabricated by shaping, e.g., a metal plate, and have three-dimensional shapes. The filament 60 is welded at one end on a resilient filament support member of the anchor 661 and at the other end on a filament support member of the support 662. The anchor 661 and the support 662 are fixed on the anode substrate 61 and are respectively connected to cathode wirings 671 and 672 functioning as take-out leads. Cathode wirings 671 and 672 can be formed as one body with the anchor 661 and the support 662, respectively. A reference numeral 62 represents a side plate made of an insulating material, e.g., a glass.
FIGS. 5B and 5C depict possible arrangements of the display region 65 and the filaments 60 as well as electrical connection of the filaments 60 to the anchor 661 and the support 662. The filaments 60 can be arranged either in a horizontal direction as shown in FIG. 5B or in a vertical direction as shown in FIG. 5C depending on a display pattern of the anode electrodes 63 as shown in FIG. 5A.
If the aspect ratio of the display region 65 is 1:2, the length of a filament 60 in case of FIG. 5B is about twice that of a filament 60 shown in FIG. 5C.
In general, the filaments 60 are fabricated by coating a core wire, made of tungsten or tungsten alloy, with carbonate for emitting thermal electrons. If an electrical current is supplied to the filaments 60, heat is generated in the filaments 60 due to their own resistance and the carbonate heated by the generated heat emits electrons. The temperature of the filaments 60 is normally maintained at about 600 to 650xc2x0 C. In case each of the filaments 60 has a thickness of about 0.64 MG (a diameter of about 15 xcexcm), a current of about 27 mA is required to maintain the filament temperature at about 600 to 650xc2x0 C. In case where a 0.64 MG filament has a length of 25 mm, its resistance value is about 48 xcexa9. Accordingly, a filament voltage should be set to be 1.3 V in order to apply the current of 27 mA through the 0.64 MG filament having the length of 25 mm.
Assuming that each filament 60 in FIGS. 5B and 5C has the thickness of 0.64 MG and that the length of each of the filaments 60 in case of FIG. 5C is 25 mm, each filament 60 in an arrangement shown in FIG. 5B will be of a length of 50 mm and, thus, a resistance thereof will be 96 xcexa9. Therefore, a filament voltage in case of FIG. 5B should be set to be 2.6 V, i.e., twice the filament voltage required in FIG. 5C.
As can be seen from the above, since a power source module having a different voltage should be prepared for every filament having a different length, the cost for the power source modules is increased, which in turn raises the manufacturing cost for the fluorescent luminous tube as well.
FIGS. 6A to 6C show various schemes conventionally employed in connecting filaments in series.
FIG. 6A illustrates an example where three filaments 60 are connected in series, in which two anchors 6611 and 6612 and two supports 6621 and 6622 are provided. The anchor 6611 and the support 6621 are connected to cathode wirings 671 and 672, respectively, and the anchor 6612 and the support 6622 are employed for making series connection of filaments 60.
FIG. 6B offers an example where five filaments 60 are connected in series, in which an anchor 6613 and a support 6623 are added to the structure shown in FIG. 6A.
FIG. 6C describes an example where seven filaments 60 are connected in series, in which an anchor 6614 and a support 6624 are further added to the structure illustrated in FIG. 6B.
As shown in FIGS. 6A to 6C, as the number of the filaments 60 is increased to be 3, 5 and 7, both the number of the anchors and the number of the supports are respectively required to be increased to be 2, 3 and 4, accordingly. As a result, the cost for manufacturing and installing the anchors and the supports and for mounting filaments thereon is increased, resulting in the increase of the whole manufacturing cost for the fluorescent luminous tube. Further, it is difficult to scale-down the anchors and the supports because they are required to have predetermined strength. Accordingly, a footprint for mounting the anchors and supports is increased, so that a dead space other than the display region becomes also increased, hampering the fabrication of a scaled down, thin and light-weighted fluorescent luminous tube.
It is, therefore, an object of the present invention to provide a fluorescent luminous tube using a single power source for various cathode filaments having different lengths and diameters and employing a connecting structure that allows cathode filaments to be easily connected in series in a reduced installation space.
In accordance with the present invention, there is provided a fluorescent luminous tube including a plurality of cathode filaments; a multiplicity of a cathode wirings, each cathode wiring including one or more terminal portions and a wiring portion and being formed of a metal layer; and one or more intermediate portions, each being made of a metal layer, wherein the cathode filament is grouped into at least one set of one or more filaments and filaments in each set are connected in series by fixing an end portion thereof on a terminal portion or an intermediate portion by ultrasonic wire bonding or ultrasonic bonding.